This invention relates to automotive brake transmission shift interlock systems of the type including an electromagnetic device for controlling the position of a shifter blocking element.
Modern automobiles equipped with automatic transmissions typically include a Park Lock feature and a Brake Transmission Shift Interlock (BTSI) feature. The operation of these features is controlled with respect to the position of a conventional ignition switch. With an ignition key inserted in the conventional ignition switch, the switch can be rotated to five different positions. These five positions are commonly referred to as the ACCESSORY, LOCK, OFF, RUN, and START positions. The ignition key can only be inserted into the ignition switch and removed from the ignition switch when the switch is disposed in the LOCK position. A counter-clockwise rotation of the ignition switch from the LOCK position moves the switch to the ACCESSORY position. A clockwise rotation of the ignition switch from the LOCK position moves the switch to the OFF, RUN, and START positions respectively.
Conventional automatic transmissions include a shifter or shift lever for selecting one of seven different operating positions. These operating positions are commonly referred to as the PARK, REVERSE, NEUTRAL, DRIVE, SECOND, and FIRST positions. An OVERDRIVE position is also provided for some transmissions.
The Park Lock feature is designed to prohibit movement of the shift lever from the PARK position unless the ignition switch is disposed in the RUN position. The Brake Transmission Shift Interlock feature is designed to prohibit movement of the shift lever from the PARK position unless the ignition switch is disposed in the RUN position and the brake pedal is depressed. With the ignition switch disposed in the RUN position, the BTSI feature is disabled when the brake pedal is sufficiently depressed to activate the brake light switch. When the BTSI feature is disabled, the shift lever may be removed from the PARK position.
As a result, a vehicle equipped with an automatic transmission cannot be placed in a condition to power the drive wheels in either a reverse or forward direction until the steering wheel has been freed for normal driving by release of the Park Lock feature and the driver has immobilized the vehicle by placing his or her foot on the brake pedal. In addition, the vehicle cannot be placed in NEUTRAL unless the key is in the ignition. This is a desired feature especially if the vehicle is parked on a slope as it could begin rolling down the slope if the vehicle is placed in NEUTRAL. It is generally believed that this combination of safety interlocks is effective in reducing accidental or inadvertent movement of a vehicle.
A first aspect of the invention is the use of the so-called xe2x80x9creverse logicxe2x80x9d to implement a BTSI using an electromagnetic device to position a blocking member to either interfere with or allow movement of the shift lever from the PARK position. It should be understood that the term xe2x80x9cshift leverxe2x80x9d, as used in this specification, is intended to embrace all known devices for xe2x80x9cselectingxe2x80x9d the operating condition of an automatic transmission including column-mounted levers working in conjunction with conventional PRNDL plates, console-mounted levers with any of various types of release mechanisms, and pushbutton selectors used in combination with what are often called xe2x80x9cshift by wirexe2x80x9d systems.
Conventional logic powers up the electromagnetic device to place the blocking member in the interfering position as soon as the ignition switch is turned on. Depression of the brake pedal de-energizes the electromagnetic device and a mechanical spring moves the blocking member out of the interfering position.
The present device reverses these conditions; i.e., the position of the blocking member, usually a metal pin, which corresponds with the unpowered condition of the BTSI is such as to inhibit or prevent movement of the shift lever out of the PARK position; consequently, depression of the brake pedal is required to power up the electromagnetic device to actively unblock the shift lever.
To permit the shift lever to be moved out of the PARK position when the battery is dead or an ignition key not available, an integral manual override mechanism is provided to permit the vehicle owner or a service person to manipulate a small lever attached to the housing of the BTSI to pull the blocking pin away from the blocking position against the force of the bias spring.
A second aspect of the invention is the provision of a xe2x80x9cdisablexe2x80x9d function for the electromagnetic device which interrupts the circuit to the device whenever the shift lever is in any position other than PARK. This eliminates the possibility of cycling the electromagnetic device during normal vehicle operation along with the clicking noise and radio interference which is associated therewith. In the preferred embodiment hereinafter described, the disable function is achieved by means of a Hall effect device mounted on the BTSI housing immediately opposite a permanent magnet on a peripheral surface of the shifter crank member such that the permanent magnet only faces and influences the Hall effect device when the crank is in the PARK position. Of course, other proximity switches, both contacting and non-contacting types, can be used for this purpose.
Another aspect of the invention involves the use of a wiring harness concept to facilitate installation of the BTSI and, in the preferred embodiment, a park detection switch (PDS) as a convenient combination. This is accomplished by replacing the normal soldered or brazed connection between the BTSI circuit board and the wires leading therefrom with a header and co-packaging therewith a park detection switch such that the wiring for the BTSI circuit board and the park detection switch run through a common harness sleeve to a multi-pin plug connector which is conveniently plugged into the automobile electrical system to make intelligence conveying contact with the ignition switch, the brake light switch and the battery.
A further aspect of the invention is the provision of an improved park detection switch which can be xe2x80x9csnapped mountedxe2x80x9d on the PRNDL plate or some other convenient location in close proximity to the BTSI housing by means of a shaped plug which dictates the proper position and simple bayonet type prongs which eliminate the need for rivets and other labor intensive fasteners.
Still another aspect of the invention is a time delay circuit for decreasing the speed of blocking member movement from the blocking or interfering position to the non-interfering position. The time delay circuit provides a less noisy or more quiet operation of the system.